A substrate processing apparatus such as a vertical substrate processing apparatus is used for heat treatment of a substrate in a process of manufacturing a semiconductor device. A predetermined number of substrates are arranged in a vertical direction and supported by a substrate retainer of a vertical substrate processing apparatus and the substrate retainer is loaded into a process chamber of the vertical substrate processing apparatus. Then, as a process gas is introduced into the process chamber with the substrate heated by a heater which is provided outside the process chamber, substrate processing such as processing of forming a thin film on the substrate is performed.
In a conventional vertical substrate processing apparatus, there is a problem in that heat is likely to leak through a lower portion of a process chamber. Specifically, there is a problem in that a lot of time is required for heating a substrate disposed on the lower portion of the process chamber to a processing temperature.